As semiconductor processes become increasingly sophisticated, the fluids used in these processes are becoming increasingly aggressive. There is an increasing risk associated with these processes that the atmosphere within a vacuum pump used to evacuate the process chamber may comprise pockets of flammable gas or, in the extreme, may be entirely flammable. Conventionally, vacuum pumps have not been designed with such environments in mind. A vacuum pumping mechanism typically comprises a metal rotor cooperating with a metal stator to convey fluid from an inlet of the vacuum pump to an outlet thereof. These components of the pumping mechanism are required to have a close tolerance so that fluid being pumped is inhibited from leaking back towards the inlet of the pump. The proximity of these two metal components is, by its very nature, inclined to represent an ignition source as any clashing of components may generate a spark. Given the aggressive nature of the processes being undertaken by these pumps, deformation of the metal components (through corrosion) is increasingly likely, so that these tolerances may be significantly reduced. Furthermore, the reactions of materials used in semiconductor processes often lead to a deposition of materials on the surfaces of the rotor and the stator. These deposits further reduce the clearances such that the alignment of the components of the pumping mechanism may be affected and clashing of the metal components may result. In addition, the deposits formed on the surfaces of the rotors and the stator may become an ignition source, for example if they are heated by friction resulting from the increased contact due to the reduced clearances.
In the event that a flammable atmosphere comes into contact with an ignition source an explosion may result. If this explosion leads to damage of the apparatus safety issues are likely to be raised. A catastrophic breach of integrity may cause projectiles to be formed from the components of the pump, creating a hazardous environment to any other equipment in the vicinity and ultimately to any personnel located in the area. If such a breach is less abrupt, leakage of flammable gas may occur into the environment surrounding the apparatus, and so if further ignition sources are available in this area, there may be a risk of further explosion. Depending on the extent of any damage caused by the explosion, the entire pumping arrangement may need to be taken out of service to permit maintenance to be undertaken. The down time for the overall process system associated with this unplanned maintenance typically results in a loss of production.
As discussed above, during operation a vacuum pumping mechanism may provide an ignition source for a flammable gas mixture. Consequently, in the event that the pumping mechanism of a vacuum pump connected to a process chamber becomes engulfed in a flammable gas mixture prior to initiation of operation of the vacuum pump, it is possible that the subsequent motion of the pumping mechanism could result in an explosion. Such an explosion could propagate back through the inlet of the pump towards the process chamber.
It is an aim of at least the preferred embodiments of the present invention to minimise the hazardous potential of such an explosion.